Electronics specs questions
Jim Pieronek
jvp%fuelrod at juliet.ll.mit.edu
Fri Nov 4 21:17:38 GMT 1994
MTN-KAT writes:
> I don't know diddly about electronics. I'm sitting here looking thru a
> Digikey catalog trying to figure out which mosfet power transistors
> and which opto-isolators to use for my project. the mosfets list
> BVdss, Ip, Idm, Vgs, Rds and PD. From my reading in Practical
> transistors and Linear IC's book, BVdss is the voltage to trigger the
> transistor. All of these mosfets are 60V-120V, obviously I'm only
> running 13.5V max, what am I missing?
>
BVdss is the breakdown voltage, drain to source, with the gate
connected to the source (N-channel enhancement-mode FET off state).
It is the voltage at which the transistor blows up, not where it turns
on. Vgs(on) or Vgs(th) is the turn-on threshold voltage - usually 2.0
to 4.0 volts. BVgs is the max. gate voltage.
> The opto-isolators list BVCEO(min), the smallest is a 7V with a
> current transfer ratio of 250%, no specs for on/off time. From my
> reading a darlington output should boost the current, the catalog
> doesn't say how much. The isolation voltage is only 3000V for this
> particular item, some list 5300V would they be better for isolating
> the engine noise from the electronics?
>
BVceo(min) is the minimum breakdown voltage from the collector to the
emitter with base open. Another blow-up parameter. Current transfer
ratio tells you what the current boost is - put 1mA into the LED on
that optoisolator and it will try to pass 2.5mA through the
transistor. Isolation voltage should be more than enough.
> I had ordered some logic level opto-isolators and they came with
> schmitt trigger outputs, I tried to run these at slow speed 0.1 sec
> and they just stayed in on mode, the data rate is supposed to be
> 1.0MHz. Could I have been hooking them up wrong?
>
Yes, this is actually possible, particularly in cases where they don't
work.
> Is there a cross-reference manual available, I have a listing for some
> logic level IGBT's, HGTP15N40C1 but Digikey doesn't have any part
> numbers similar to this. The MOSFETs have a part number, IRF540, once
> again no similar numbers in the catalog.
>
IRF540-ND is in the Digi-Key catalog. Look on the page with
International Rectifier HEXFETs.
More information about the Diy_efi
mailing list